The present invention relates to azeotrope-like compositions consisting essentially of difluoromethane, pentafluoroethane, 1,1,1,2-tetrafluoroethane and a hydrocarbon selected from the group consisting of: n-butane; isobutane; n-butane and 2-methylbutane; n-butane and n-pentane; isobutane and 2-methylbutane; and isobutane and n-pentane.
In recent years it has been pointed out that certain kinds of fluorinated hydrocarbon refrigerants released into the atmosphere may adversely affect the stratospheric ozone layer. Although this proposition has not yet been completely established, there is a movement toward control of the use and the production of certain chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) under an international agreement. Accordingly, there is a demand for the development of refrigerants that have a lower ozone depletion potential than conventional CFC and HCFC-based refrigerants while still achieving acceptable performance in refrigeration applications. Hydrofluorocarbons (HFCs) are gaining acceptance as replacements for CFCs and HCFCs as HFCs contain no chlorine and, therefore, have zero ozone depletion potential.
Mineral oils and alkylbenzenes have been conventionally used as lubricants in CFC-based refrigeration systems. However, the lack of solubility of these lubricants in HFC-based refrigerants has precluded their use and necessitated development and use of alternative lubricants for HFC-based refrigeration systems, which utilize polyalkylene glycols (PAGs) and polyol esters (POEs). A lubricant change from mineral oil or alkyl benzene to POE or PAG lubricants (which increases expenses in the refrigeration indusrty) is required when the HFC mixtures are used to replace CFC-based refrigerants. While the PAGs and POEs are suitable lubricants for HFC-based refrigeration systems, they are extremely hygroscopic and can absorb several thousand ppm (parts per million) of water upon exposure to moist air. This absorbed moisture leads to problems in the refrigeration system, such as formation of acids which causes corrosion of the refrigeration system, and the formation of intractable sludges. Conversely, mineral oils and alkylbenzenes are much less hygroscopic and have low solubility, less than 100 ppm, for water. Additionally, PAG and POE lubricants are considerably more expensive than the hydrocarbon lubricants, typically on the order of three to six times more expensive. Consequently, there is a need and an opportunity to resolve this solubility problem so that the refrigeration industry may utilize mineral oil and alkylbenzene lubricants with HFC-based refrigerants.
In refrigeration apparatus, refrigerant may be lost during operation through leaks in shaft seals, hose connections, soldered joints and broken lines. In addition, the refrigerant may be released to the atmosphere during maintenance procedures on refrigeration equipment. If the refrigerant is not a pure component or an azeotropic or azeotrope-like composition, the refrigerant composition may change when leaked or discharged to the atmosphere from the refrigeration apparatus, which may cause the refrigerant remaining in the equipment to become flammable or to exhibit unacceptable refrigeration performance. Accordingly, it is desirable to use as a refrigerant a single fluorinated hydrocarbon or an azeotropic or azeotrope-like composition which fractionates to a negilgible degree upon leak from a refrigeration apparatus.
In refrigeration applications where the potential of fire or fire""s toxic byproducts are a concern, it is desirable for refrigerant compositions to be nonflammable in both liquid and vapor phases, when charging fresh refrigerant to a system or after refrigerant has leaked from a system.
Accordingly, there is a need in the refrigeration industry for compositions that are non-ozone depleting, nonflammable, and essentially non-fractionating azeotrope-like compositions. Additionally, there is a need in the refrigeration industry for compositions that offer improved return of conventional-refrigeration lubricating oils from non-compressor to compressor zones in compression-refrigeration apparatus, as well as superior refrigeration performance.
The compositions of the present invention satsify the aforementioned needs confronting the refrigeration industry. The present compositions are useful as refrigerants, and in particular as HCFC-22 alternatives. Unlike compositions containing propane and pentane, compositions of the present invention are non-flammable in both liquid and vapor phasesxe2x80x94as intially formulated and during leakage. The present invention is directed to azeotrope-like compositions consisting essentially of from about 1 to about 19 weight percent difluoromethane (HFC-32), from about 25 to about 60 weight percent pentafluoroethane (HFC-125), from about 24 to about 60 weight percent 1,1,1,2-tetrafluoroethane (HFC-134a) and from about 0.5 to about 5 weight percent of a hydrocarbon, wherein said hydrocarbon is selected from the group consisting of: n-butane; isobutane; n-butane and 2-methylbutane; n-butane and n-pentane; isobutane and 2-methylbutane; and isobutane and n-pentane.
The azeotrope-like compositions of the present invention consist essentially of difluoromethane (HFC-32, CH2F2, normal boiling point of xe2x88x9251.7xc2x0 C.), pentafluoroethane (HFC-125, CF3CHF2, normal boiling point of xe2x88x9248.5xc2x0 C.), 1,1,1,2-tetrafluoroethane (HFC-134a, CF3CHF2, normal boiling point of xe2x88x9226.1xc2x0 C.) and a hydrocarbon selected from the group consisting of: n-butane (CH3CH2CH2CH3, normal boiling point of xe2x88x920.5xc2x0 C.); isobutane (CH(CH3)3, normal boiling point of xe2x88x9211.8xc2x0 C.); n-butane and 2-methylbutane (CH3CH2CH(CH3)2, normal boiling point of 27.9xc2x0 C.); n-butane and n-pentane (CH3CH2CH2CH2CH3, normal boiling point of 35.9xc2x0 C.); isobutane and 2-methylbutane; and isobutane and n-pentane.
The azeotrope-like compositions of the present invention consist essentially of from about 1 to about 19 weight percent difluoromethane, from about 25 to about 60 weight percent pentafluoroethane, from about 24 to about 60 weight percent 1,1,1,2-tetrafluoroethane and from about 0.5 to about 5 weight percent of a hydrocarbon, said hydrocarbon selected from the group consisting of: n-butane; isobutane; n-butane and 2-methylbutane; n-butane and n-pentane; isobutane and 2-methylbutane; and isobutane and n-pentane. The preferred azeotrope-like compositions of the present invention consist essentially of from about 1 to about 15 weight percent difluoromethane, from about 30 to about 50 weight percent pentafluoroethane, from about 30 to about 50 weight percent 1,1,1,2-tetrafluoroethane and from about 1 to about 4 weight percent of the aforementioned hydrocarbons. The most preferred azeotrope-like compositions of the present invention consist essentially of 1-9 weight percent difluoromethane (HFC-32), 30-50 weight percent pentafluoroethane (HFC-125), 30-50 weight percent 1,1,1,2-tetrafluoroethane (HFC-134a) and 1-4 weight percent of the aforementioned hydrocarbons.
As previously stated, in refrigeration apparatus, refrigerant may be lost during operation through leaks in shaft seals, hose connections, soldered joints and broken lines. Additionally, the refrigerant may be released to the atmosphere during maintenance procedures on refrigeration equipment. If the refrigerant is not a pure component or an azeotropic or azeotrope-like composition, the refrigerant composition may change when leaked or discharged to the atmosphere from the refrigeration apparatus, which may cause the refrigerant remaining in the equipment to become flammable or to exhibit unacceptable refrigeration performance. Accordingly, it is desirable to use as a refrigerant a single fluorinated hydrocarbon or an azeotropic or azeotrope-like composition, such as the present invention, which fractionates to a negilgible degree upon leak from a refrigeration apparatus.
By azeotrope-like composition is meant a constant boiling, or substantially constant boiling, liquid admixture of two or more substances that behaves as a single substance. One way to characterize an azeotrope-like composition is that the vapor produced by partial evaporation or distillation of the liquid has substantially the same composition as the liquid from which it was evaporated or distilled, that is, the admixture distills/refluxes without substantial composition change. Another way to characterize an azeotrope-like composition is that the bubble point vapor pressure and the dew point vapor pressure of the composition at a particular temperature are substantially the same. Herein, a composition is azeotrope-like if, after 50 weight percent of the composition is removed, such as by evaporation or boiling off, the difference in vapor pressure between the original composition and the composition remaining after 50 weight percent of the original composition has been removed is less than about 10 percent.
By effective amount is meant the amount of each component of the inventive compositions which, when combined, results in the formation of an azeotrope-like composition. This definition includes the amounts of each component, which amounts may vary depending on the pressure applied to the composition so long as the azeotrope-like compositions continue to exist at the different pressures, but with possible different boiling points. Therefore, effective amount includes the amounts, such as may be expressed in weight percentages, of each component of the compositions of the instant invention, which form an azeotrope-like composition at temperatures or pressures other than as described herein.
The azeotrope-like compositions of the present invention can be prepared by any convenient method including mixing or combining effective amounts of components. A preferred method is to weigh the desired component amounts, and thereafter, combine them in an appropriate container.
A surprising result, and an important feature of the present compositions, is that they remain nonflammable in both the vapor and liquid phases before and after the compositions leak from a container. Based on standard flammability test method ASTM 681 at 100xc2x0 C., the following flammability limits have been determined:
The data show compositions with a higher amount of HFC-125 can tolerate more hydrocarbon and still be nonflammable. Also, HFC-32 is about 10 times less flammable than hydrocarbons. To give an indication of mixture flammability, the following formula gives an approximation of the xe2x80x9ctotal equivalent hydrocarbonxe2x80x9d (THE) present in mixtures that contain both HFC-32 and hydrocarbons: TEH=HC+R32/10, where TEH=Total Equivalent Hydrocarbon in weight percent, HC=weight percent hydrocarbon in a mixture, and R32=weight percent HFC-32 in a mixture. For the compositions of the present invention, it is useful to relate the amount of HFC-125 in the mixture to flammability because HFC-125 has some degree of flame suppression. Table 1 indicates the flammability limit of a mixture containing both HFC-32 and hydrocarbons based on HFC-125 composition and TEH.
Additives known in the refrigerants field such as lubricants, corrosion inhibitors, surfactants, stabilizers, anti-foam agents, dyes and other appropriate materials may be added to, and used in the presence of, the present compositions of the invention for a variety of purposes, provide that such additives do not have an adverse influence on the present compositions for their intended application or change the basic and novel characteristics of the present invention as claimed.
Although the present specification is directed to use of the present azeotrope-like compositions as compression refrigerants, the present compositions may also find utility as cleaning agents, expansion agents for polyolefins and polyurethanes (polymer foam blowing agents), aerosol propellants, heat transfer media, gaseous dielectrics, power cycle working fluids, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents and displacement drying agents.